It is proposed that cytological, histologicad and biochemical studies on tissues of insecticide-resistant populations of Gambusia aaffinis (mosquitofish) exposed to organochlorine compounds be conducted and compared with parallel studies of insecticide-susceptible populations and with controls. Biochemical and certain histological studies will be conducted in the Zoology Department at Mississippi State University. The electron microscopic work will be conducted in the Biology Deapartment at the University of Alabama. Information derived from these studies will be applicable to an understanding of the cellular adaptive processes of this vertebrate in response to chronic environmental stress, and towards prediction of changes taking place in other vertebrate. This understanding can lead toward the development of guidelines in planning invertebrate control programs. Specific parameters to be measured include lipid deposition in tissue, myelin redundancy cytological effects of organochlorine compound exposure on nervous tissue, and endoplasmic reticular membrane and enzyme responses to organochlorine compound exposure. These studies could provide an understanding of the cellular basis of vertebrate insecticide resistance.